Remote vehicle data interface tag system

ABSTRACT

A vehicle information system including a tag system mounted in a vehicle. The tag system transmits vehicle-related data acquired from the vehicle to an interrogator. The vehicle information system utilizes a bus in the vehicle with low-cost RF communications in the tag system and an interrogator to remotely access the vehicle-related data as the vehicle exits or enters a designated area. The interrogator provides the vehicle-related data acquired from the tag system to a host computer.

FIELD OF THE INVENTION

This invention relates to systems for processing vehicle information andin particular to a system for automating the acquisition and transfer ofinformation from a vehicle.

BACKGROUND OF THE INVENTION

Some suggestions have been made in the past to employ availabletechnology for the purpose of automating transactions concerningvehicles. For example, U.S. Pat. No. 5,058,044 (the '044 patent) toStewart et al. suggests a system that includes a processing systemon-board a vehicle for gathering data related to the operational historyof the vehicle and transferring the data to a stationery processingsystem. The system provides information to a mechanic regarding neededrepairs and automates commercial transactions such as the billing ofvehicle rentals or of repair work to an owned/leased vehicle. Theon-board system includes a processor for collecting data from sensorsassociated with selected operations systems of the vehicle (e.g.,lights, drive train, tires, and fluid levels). Depending upon the systemmonitored, the processor may continually update its condition (e.g.,mileage and gas level) in a storage area or it may only storeinformation when service is required (e.g., lights and drive train).When the vehicle enters a service area, the on-board system isinterrogated for its stored information. The interrogation is executedby an annunciator system which first detects the physical presence ofthe vehicle and then transmits an RF interrogation signal to a receiveron-board the vehicle and coupled to the on-board processor. If theinterrogation signal is recognized by the on-board processor, a vehicleidentification code along with the stored information in converted to anRF signal and transmitted from the vehicle. The '044 patent isincorporated herein by reference.

The system described in the '044 patent connects the on-board processorto each of the components in the vehicle. As a result, the vehicle mayhave to be substantially modified to accommodate the system described inthe '044 patent. Further, the vehicle includes a receiver and atransmitter. As a result, the cost and complexity of the system isincreased.

SUMMARY OF THE INVENTION

The present invention provides a vehicle information system including atag system mounted in a vehicle. The tag system transmitsvehicle-related data acquired from the vehicle to an interrogator. Thevehicle information system utilizes a bus in the vehicle with low-costRF communications in the tag system and an interrogator to remotelyaccess the vehicle-related data as the vehicle exits or enters adesignated area. The interrogator provides the vehicle-related dataacquired from the tag system to a host computer.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, but are notrestrictive, of the invention.

BRIEF DESCRIPTION OF THE DRAWING

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawing. It is emphasizedthat, according to common practice, the various features of the drawingare not to scale. On the contrary, the dimensions of the variousfeatures are arbitrarily expanded or reduced for clarity.

Included in the drawing are the following figures:

FIG. 1 is a block diagram of a vehicle information system 10 accordingto an exemplary embodiment of the present invention.

FIG. 1A is a diagram of a shuttle including an interrogator 300Aaccording to an exemplary embodiment of the present invention.

FIG. 2 is a block diagram of a vehicle 100 including a tag system 120Baccording to an exemplary embodiment of the present invention.

FIG. 3A is a block diagram of the tag system 120B according to anexemplary embodiment of the present invention.

FIG. 3B is a flow chart diagram useful for illustrating the operation ofthe processor 205.

FIG. 4 is a diagram illustrating the contents of a message packet 400transmitted from the tag system 120B according to an exemplaryembodiment of the present invention.

FIG. 5 is a timing diagram illustrating Manchester encoding.

FIG. 6 is a block diagram of an interrogator 300B according to anexemplary embodiment of the present invention.

FIG. 7 is a timing diagram illustrating the transmission of messagepackets 400 from different tag systems 120C-120E according to anexemplary embodiment of the present invention.

FIG. 8 is a data diagram illustrating the time intervals in which themessage packets 400 are transmitted from the tag system 120B.

FIG. 9 is a block diagram of the processor 510 according to an exemplaryembodiment of the present invention.

FIG. 10 is a timing diagram illustrating the operation of the integrator505.

FIG. 11 is a timing diagram illustrating the operation of thediscriminator 510.

FIG. 12 is a diagram illustrating the start of frame sequence.

FIG. 13 is a diagram illustrating the end of frame sequence.

DETAILED DESCRIPTION OF THE INVENTION Overview

Referring now to the drawing, wherein like reference numerals refer tolike elements throughout, FIG. 1 shows a vehicle information system 10including a tag system 120B mounted in a vehicle 100. The tag system120B transmits vehicle-related data acquired from the vehicle 100 to aninterrogator 300B. The vehicle information system 10 utilizes a bus 110(shown in FIG. 2) in the vehicle 100 with low-cost RF communications inthe tag system 120B and the interrogator 300B to remotely access thevehicle-related data as the vehicle n100 exits or enters a designatedarea 20. The interrogator 300B provides the vehicle-related dataacquired from the tag system 120B to host computer 320.

The vehicle-related data includes, for example, temperature, fluidslevels, oil pressure, odometer, and other data related to the vehicle100. The tag system 120B may also be used to read the status ofemissions-related and safety-related parameters without having todirectly connect any equipment to the vehicle.

The tag system 120B includes only an RF transmitter 210 (shown in FIG.3A) for transmitting the vehicle-related data. The interrogator 300Bincludes only an RF receiver 305 (shown in FIG. 6) for receivingvehicle-related data. As a result, the cost and complexity of the tagsystem 120B and the interrogator 300B may be reduced because the tagsystem 120B and the interrogator 300B each do not include circuitry andsoftware to both transmit and receive data. In an alternativeembodiment, the tag system 120B and the interrogator 300B may eachinclude a transmitter and receiver for transmitting and receiving data.

The tag system 120B only monitors data transmitted on the bus 110 and,as a result, the control and operation of the bus 110 does not have tobe modified to accommodate the tag system 120B. In this way, the tagsystem 120B may be integrated into the vehicle 100 with minimalmodification to the vehicle 100. Thus, the vehicle information system 10is more likely to be accepted and incorporated into vehicles 100 byvehicle manufacturers. In an alternative embodiment, the tag system 120Bmay transmit data on the bus 110.

The vehicle information system 10 may be utilized in a variety ofenvironments to remotely monitor vehicles. For example, the vehicleinformation system 10 may be used to determine the speed of a vehicle.In this case, the tag system 120B repeatedly transmits the speed andvehicle identification data of the vehicle 100 as it travels along aroad. An interrogator 300B positioned adjacent to the road receives thetransmitted data for subsequent processing.

Alternatively, the vehicle information system may be used to monitortrucks as they leave and arrive at a central terminal. In this case, theinterrogator 300B may be located at access points to the centralterminal to acquire data transmitted from tag systems 120B coupled tothe trucks. The host computer 320 uses the data acquired from theinterrogator 300B to determine which trucks have entered and exited thecentral terminal.

In another alternative embodiment, the vehicle information system 10 maybe used in a vehicle rental system. The operation of the vehicleinformation system 10 is described below in the context of the vehiclerental system.

Description of the Exemplary Embodiments

FIG. 1 shows a vehicle information system 10 including a tag system 120Bmounted in vehicle 100. The tag may be mounted in an area not visible tothe casual observer. Mounting locations could be any area that is notcompletely enclosed by metallic surfaces. For example, suitablelocations include behind the dashboard in the passenger compartment,behind bumpers, or behind non-metallic body parts, or beneath thevehicle. The vehicle 100 may be, for example, a rental vehicle locatedat an airport. A person renting the vehicle 100 (hereinafter "therenter") is provided a driver tag system 120A upon his arrival at theairport. The driver tag system 120A includes stored data identifying therenter and the vehicle that has been rented. The driver tag system 120Aincludes circuitry for transmitting the stored data.

As is shown in FIG. 1A, after receiving the driver tag system 120A, therenter boards a shuttle 40 to travel to the rental lot where the vehicle100 is located. The shuttle 40 includes an interrogator 300A foracquiring the data transmitted from the driver tag system 120A. Theacquired data is transmitted to the host computer 320 which notifies thedriver of the shuttle 40 where the vehicle 100 is located in the rentallot. The host computer 320 maintains a database of rental dataidentifying the renter, the vehicle 100 rented, and other data relatedto the vehicle 100. For example, the other data may include the locationof the vehicle 100 in the rental lot and the fuel level and the odometerreading of the vehicle 100.

Returning to FIG. 1, the renter is dropped by the vehicle 100, entersthe vehicle 100, and drives to the exit of the rental lot. The tagsystem 120B located in the vehicle 100 intermittently transmits messagedata packets 400 (shown in FIG. 4). The interrogator 300B receives themessage packets 400 when the vehicle 100 is in the designated area 20.The size of the designated area 20 may be adjusted by increasing thestrength of the signal transmitted from the tag system 120B orincreasing the sensitivity of the RF receiver 305 (shown in FIG. 6) inthe interrogator 300B. The interrogator 300B has an antenna (not shown)that is oriented so that one or more message packets 400 transmittedfrom the tag system 120B may be received as the vehicle 100 passesthrough the designated area 20. The interrogator 300B may be a hand helddevice or permanently mounted. For each installation, such as anairport, there is a link via radio or hard wired, from the interrogator300B to the host computer 320.

As is shown in FIG. 4, the tag system 120B transmits different types ofdata in the message packet 400. The message packet 400 includes vehicleidentification data (VID) 415 such as a vehicle identification number(VIN) that uniquely identifies the vehicle 100. The message packet 400may also include vehicle-related data such as fuel data 420 indicatingthe fuel tank level and odometer data 425 indicating the odometerreading.

As is shown in FIG. 2, the vehicle 100 includes the tag system 120B. Thevehicle 100 includes a bus 110 that is used to transmit data between afuel tank system 130, an instrument panel 140, other modules 150, and avehicle computer 160. The module 150 is an interface with othercomponents, for example, the engine (not shown) in the vehicle 100. Thevehicle computer 160 may be, for example, the body or engine computer inthe vehicle 100.

Data is provided to and retrieved from the bus 110 in accordance with avehicle bus standard such as the Society of Automotive Engineers (SAE)J1850 standard or the Controller Area Network (CAN) standard. The SAEJ1850 standard defines an electrical and data protocol for the bus 100and the components coupled to the bus such as the fuel tank system 130,the instrument panel 140, the module 150, and the vehicle computer 160.The bus 100 is, for example, a single wire loop. The fuel tank 130, theinstrument panel 140, the module 150, and the vehicle computer 160provide data to or retrieve data from the bus 110.

The inventors have recognized that it may not be advantageous to provideadditional components that transmit data on the bus 110. Vehiclemanufactures have designed the bus 110 and the components coupled to thedata bus 110 to ensure the reliable transmission of data. The additionof components that transmit data on the data bus 110 may requireadjustments in the operation of the other components to ensure reliabletransmission of data.

The tag system 120B avoids these problems because the tag system 120Bonly monitors data that is transmitted on the data bus 110. The tagsystem 120B may be coupled to the bus 110 by, for example, crimping aconnector on the wire forming the bus 110 and connecting the connectorto the tag system 120B. As a result, the operation of the bus 110 doesnot have to be modified. In this way, the tag system 120B may beintegrated with minimal modification of the vehicle 100. In addition,vehicle manufactures may be more willing to incorporate the tag system120B in the vehicle 100 because it does not require modification of thebus 110 or the components attached to the bus 110. Further, theinstallation costs of the tag system 120B are minimized because onlyminor modifications may be required to install the tag system 120B. Inan alternative embodiment, the tag system 120B may transmit data on thebus 110.

The tag system 120B determines the status of different componentsattached to the bus 110 by monitoring the data transmitted from thosecomponents on the bus 110. For example, the fuel tank system 130includes circuitry for determining the fuel level in the fuel tank as iswell known and transmits this data on the bus 110 for subsequent displayon a level gauge (not shown) in the instrument panel 140. The tag system120B retrieves the transmitted data from the bus 110 and transmits thefuel level to the interrogator 300B. As a result, the tag system 120Bmay provide the fuel level without using any specialized circuitry formonitoring the fuel level or directly coupling the tag system 120B tothe circuitry that measures the fuel level.

The tag system 120B may also be coupled to different components in thevehicle 100. As is described in greater detail below, the tag system120B may include, for example, circuitry for determining the odometerreading of the automobile by monitoring data provided from a wheelsensor.

The tag system 120B is described in greater detail below with referenceto FIG. 3A. The tag system 120B includes an interface 200 that iscompliant with the SAE J1850 standard and provides an interface betweenthe tag system 120B and the bus 110. The interface 200 is coupled to thebus 110 and only retrieves data from the bus 110. Alternatively, theinterface 200 may provide data to the bus 110. Data that is transmittedon the bus 110 by the components coupled to the bus 110 includesidentification data that identifies which component transmitted the dataon the bus 110. For example, the fuel tank system 130 (shown in FIG. 2)transmits a data packet on the bus 110 that indicates that the data wastransmitted from the fuel tank 130. In addition, the data packet mayinclude data indicating the amount of fuel in the fuel tank. Further,the data packet may include data indicating which of the othercomponents coupled to the bus 110 should receive the transmitted datapacket. For example, the data packet may include data indicating thatthe instrument panel 140 should retrieve the transmitted data packetfrom the fuel tank system 130.

The data acquired from the bus 110 is provided to processor 205 whichis, for example, a micro-controller. The interface 200 and the processor205 may be combined as a single component. One such exemplarycombination of the interface 200 and the processor 205 is part numberMC68HC05V7 available from Motorola. This particular part is compatiblewith General Motors automobiles compliant with the SAE J1850 standard.The operation of the processor 205 is described below with reference toFIG. 3B.

As is shown in FIG. 3B, at step S100, the data packets are retrievedfrom the bus 110 and provided to the processor 205. At step S110, theprocessor 205 determines if the retrieved data packet is to be furtherprocessed. If not, step S100 is repeated. The processor 205 determineswhether the bus data packet is to be further processed by examining theidentification data of the data packet. For example, if the data packetis from the fuel tank system 130, the processor 205 selects this datapacket for further processing. The processor 205 does not furtherprocess the data packet if it is from, for example, the vehicle computer160. Which data packets are to be processed can be determined using alookup table (LUT) (not shown) provided in the processor 205. The LUTmay include data indicating the data packets to be selected for furtherprocessing. For example, the LUT may include data indicting that datapackets from the fuel tank system 130 and the instrument panel 140should be selected for further processing.

The processor 205 may also receive data from an analog-to-digital (A/D)converter 215 (shown in FIG. 3A) which is coupled directly to acomponent in the vehicle 100. For example, the A/D converter 215 may becoupled directly to a sensor 155 that measures the fuel level as isdescribed in the '044 patent and which is not coupled to the bus 110. Inthis case, the A/D converter 215 converts the analog signals from thesensor 155 to digital signals for further processing by the processor205. The processor 205 determines the fuel level based on the fuelsensor readings. Alternatively, the processor 205 may recover data fromother components in the vehicle 100 that do not require conversion bythe A/D converter 215. In other words, the components may providedigital data directly to the tag system. In this case, these componentswould be coupled directly to the processor 205.

Returning to FIG. 3B, at step S120, the vehicle-related data isretrieved from the data packet. At step S130, the processor 205 producesa message packet 400 (shown in FIG. 4). At step S 140, the processor 205modulates the RF transmitter 210 to transmit the message packet 400. TheRF transmitter 210 is, for example, an AM surface acoustic wave (SAW)transmitter. The modulated signal is produced by the processor 205turning the transmitter 210 on and off.

The RF link between the tag system 120B and the interrogator 300B may beimplemented using either active or "semi-active" transmissiontechnology. In active transmission systems, the tag system 1208 uses abattery 170 (shown in FIG. 2) to power the entire tag system 120B. In asemi-active transmission system, the tag system 120B uses battery powerfor the tag system 120B except for the transmitter 210. Message packets400 may be transmitted between the tag system 120B and the interrogator300B via passive backscatter where a constant wave is transmitted fromthe interrogator 300B, passively modulated, and reflected back from thetag system 120B to the interrogator 300B as is known.

The RF link may provide either one-way, the tag system 120B to theinterrogator 300, or two way communication. A one way link provides amonitoring function where the tag system 120B reports current conditionof all monitored parameters of the vehicle 100 as described above. Atwo-way link allows the interrogator 300B to send messages to the tagsystem 120B to either command the tag system 120B to monitor certainparameters, or to pass parameters to systems in the vehicle 100. In thelatter case, the link may provide the means to remotely performfunctions such as lock/unlock doors and monitor/adjust emission controlsensors and systems.

As is shown in FIG. 5, the RF transmitter 210 is modulated usingManchester encoding. As is well known in the art of data transmissionand as is described in Simon Haykin, Communication Systems, pp. 414-15(2nd ed. 1983), clock data and the data to be transmitted may be encodedusing Manchester encoding to produce a signal which includes both themessage packet 400 and the clock data. The width 2t of the data pulsesto be encoded is twice the width t of the Manchester encoded data. As aresult, the Manchester encoding effectively doubles the bandwidth of thesignal to be transmitted. As is described in greater detail below, theintegrator 300B recovers both the clock data and the data from theManchester encoded signal.

As is shown in FIG. 4, the processor 205 can transmit one or moremessage packets 400 including data for different components in thevehicle 100 (shown in FIG. 1). The message packet 400 includes a datatype field 405 that indicates what type of data, for example, fuel andodometer, is contained in the packet. The message packet 400 includessequence data 410 that indicates whether the message packet 400 is asingle message packet or one of a sequence of related message packetsand indicates the position of the message packet 400 in the sequence ofrelated message packets. Related message packets 400 are provided toreduce the size of the message packets. The size of the message packet400 is decreased to provide for transmissions from a number of differenttag systems 120B. The packet also contains a unique identification field415, which may be the VID, such that the interrogator can group togethermultiple packets from the same vehicle.

In order to reduce the complexity and cost of the tag systems, thenumber of frequencies for transmission may be limited and may be, forexample, one frequency. Thus, in environments where there are a numberof vehicles 100 including tag systems 120B, the packet size is reducedto minimize the time for transmitting the message packet 400. In thisway, the likelihood of more than packet 400 being transmitted at onetime is reduced. By separating large data transmissions into multiplepackets 400 interference is reduced.

A sequence of message packets 400 may be used to provide data relatingto the vehicle 100 that include more bits than are provided in a singlemessage packet 400. The packet type data 405 and the packet sequencedata 410 are, for example, each one (1) byte. The message packet 400 mayalso include vehicle identification data (VID) which may be a uniquesequence of numbers, letters, or symbols used to identify a particularvehicle 100. For example, the VID 415 may be the vehicle identificationnumber (VIN). The VID 415 is, for example, thirteen (13) bytes. Acompression algorithm may be used in order to reduce the number of bitsin the VID 415.

Data related to the vehicle 100 is also provided in the message packet400. For example, the message packet includes fuel data 420 and odometerdata 425. The fuel data 420 indicates the amount of remaining fuel inthe fuel tank of the vehicle 100. The odometer data indicates thecurrent mileage the vehicle 100 has traveled. The fuel data 420 and theodometer data 425 each are, for example, two (2) bytes. Extra data 430may be contained in the message packet 400 for providing additional dataregarding the vehicle 100. The extra data 430 may include, for example,data indicating the status of the engine or whether the vehicle 100 hasbeen in a collision. For the case where the vehicle 100 has been in acollision, the tag system 120B receives data from one or more sensors(e.g. accelerometer (not shown)) in the vehicle 100 that detect impactsto the vehicle 100. The extra data 430 may also include informationregarding the rental of the vehicle 100. The message packet 400 alsoincludes an error correction code 435, which is, for example, two (2)bytes. The message packet 400 may also transmit only VID 415. In thiscase, the tag system may not be coupled to the bus 110.

The message packet 400 is transmitted from the tag system 120B in arange of zero (0) to X seconds where X is, for example, one half(1/2).Further, the message packets 400 are transmitted one (1) to two (2)percent of the time. The message packets 400 are also transmitted duringone of Y time slots. For example, consider FIG. 7 which illustrates themessage packets 400 transmitted from three different tag systems 120C,120D, and 120E which are the same as the tag system 120B.

As is describe above, a collision between the message packets 400 isminimized by reducing the size of the message packets 400. As is shownat time T1, however, two of the message packets 400 may be transmittedat the same time from two different tag systems 120C and 120D. In thiscase, the interrogator 300B receives segments of two message packetsand, as a result, determines that the received transmission is invalid.The operation of the interrogator 300B when receiving message packets400 is described in greater detail below. If the message packets 400where transmitted at a constant time interval from each tag system 120Cand 120D, then the message packets 400 from each tag system 120C and120D would continually be transmitted at the same time.

In order to avoid this problem, the retrieved data is transmitted at afixed average packet transmission rate, however, the time differentialbetween transmission of individual packets varies. One means ofaccomplishing this is for exemplary processor 205 (shown in FIG. 3A) totransmit the message packets in one of sixteen random time slots S1-S16shown in FIG. 8. The particular time slot in which a packet is sent isselected in response to a random number generated in processor 205. As aresult, the time interval ΔT1, ΔT2, and ΔT3 may vary between eachmessage packet 400 transmitted from the tag system 120C. Accordingly,although message packets 400 transmitted from tag systems 120C and 120Dmay collide at time T1, subsequent message packets 400 transmitted fromthe tag systems 120C and 120D are not likely to be transmitted at thesame time. Thus, numerous tag systems 120B transmitting at the samefrequency may be used in close proximity to each other. As a result, thecost of the tag systems 120C-120E may be reduced because a variety oftag systems 120C-120E transmitting at different frequencies do not haveto be provided. Further, the cost of the interrogator 300B may bereduced because it may be designed to receive transmissions at onefrequency instead of multiple frequencies. Alternatively, the tagsystems 120C-120E may transmit at different frequencies. In this case,the interrogator 300B would include circuitry to receive transmissionsat different frequencies.

In an alternative embodiment, the tag system 120B may monitor thevoltage level of the battery 170 (shown in FIG. 1) to determine howoften to transmit a message packet 400. Typically, a charge is appliedto the battery 170 when a vehicle 100 is in motion. In contrast, areduced charge or no charge at all is applied to the battery 170 whenthe vehicle 100 is idling or turned off. Thus, the tag system 120B maymonitor the difference between the voltage levels to determine whetherthe vehicle 100 is moving. The tag system 120B monitors the voltagelevel using data retrieved from bus 110 or from a direct connection to asensor (not shown) coupled to the battery 170.

The tag system 120 may increase the transmission rate of the messagepackets 400 when the vehicle 100 is moving. In this way, a number ofmessage packets 400 may be transmitted as the vehicle 100 passes throughthe designated area 20. Thus, the likelihood of the interrogator 300Breceiving a message packet 400 is increased. The tag system 120B maydecrease the transmission rate of the message packets 400 when thevehicle is not moving. In this way, a number of message packets 400 maybe transmitted in the designated area 20 while reducing the total numberof message packets 400 transmitted in a specific period of time. Thus,the likelihood of a collision between message packets 400 is reduced.

Returning to FIG. 1, the interrogator 300B receives data transmittedfrom the tag system 120B including the fuel data 420 and the odometerdata 425 when the vehicle 100 enters the designated area 20. The VID415, the odometer data 420, and the fuel data 425 are provided to thehost computer 320 for storage and processing. In addition, theinterrogator 320 receives the data transmitted from the driver tagsystem 120A.

The host computer 320 determines whether the vehicle 100 and the renterare "matched" based on the data transmitted from the tag system 120B andthe driver tag system 120A. The renter and the vehicle 100 are matchedif the stored data indicates that the renter has rented the vehicle 100exiting the rental lot. If there is a match, the host computer providesa signal to access/exit system 30 to allow the vehicle 100 to exit therental lot. If there is not a match, the renter is instructed to returnto the rental lot for assistance.

In an alternative embodiment, a user interface 165 may be coupled to thebus 110 or directly to the tag system 120B. The user interface 165 maybe used by the renter to enter an access code, credit card number, orother information which is acquired by the tag system 120B directly orfrom the bus 110. The user interface 165 is, for example, a key pad,card reader, or other well known device for providing data to a systemfrom an external source. In operation, for example, the user interface165 may be used to acquire the renter's credit card number. The tagsystem 120B transmits the credit card number to the interrogator 300B.The credit card number is used to verify that the renter and the vehicle100 match. If there is a match, the vehicle is allowed to leave therental lot. If there is no match, the vehicle is not permitted to leavethe lot.

After exiting the rental lot and upon returning to the rental lot ordrop-off point, the interrogator 300B receives the message packet 400transmitted from the tag system 120B. The host computer 320 compares thefuel data 420 and the odometer data 425 from the tag system 120B to thedata stored in the database. The host computer 320 uses the differencebetween the fuel data 420 from the tag system 120B when the vehicle wasexiting the rental lot to the fuel data 425 from the tag system 120Bwhen the vehicle 100 is returned to the rental lot to determine if therenter should be charged for gasoline. Similarly, the odometer data 425is utilized to determine if the renter should be charged for the mileagethe vehicle has traveled. A receipt is generated and provided to therenter. The renter then parks the vehicle. Alternatively, the renter mayreceive the receipt after the vehicle is parked.

As is shown in FIG. 6, the transmitted message packet 400 (shown in FIG.4) is received by interrogator 300B. The interrogator 300B includes anRF receiver 305 that receives the transmitted message packet 400. Thereceived message packet 400 is provided to demodulator 310 thatdemodulates the received message packet 400. The processor 315 processesthe received message packet and converts the data provided in themessage packet 400 to a form suitable for use by the host computer 320.

FIG. 9 is a block diagram of the processor 315. The processor 315includes an integrator 505 that integrates the data over time. It has amaximum threshold MAX1 of for example, 208 counts and a minimumthreshold MIN1 of for example, zero (0) counts. Moreover, it has abuilt-in hysteresis and a low-high threshold TRH of, for example, 187counts, and a high-low threshold TRL of for example, 21 counts. Theabove exemplary values are for a 9600 baud rate transmission. Every timeone of these thresholds is reached, a "start" pulse is generated forsynchronization of the subsequent circuitry. The demodulated signalDATA₋₋ IN is provided to the integrator 505 which implements anintegration operation to reduce the effect of high frequency noise inthe demodulated signal DATA₋₋ IN. In other words, the integrator 505implements a low pass filter operation. The integrator 505 includes acounter 507 which counts up when the demodulated signal DATA₋₋ IN ishigh and counts down when the demodulated signal DATA₋₋ IN is low.

The operation of the integrator 505 is described below with reference toFIG. 10. At time T1, the counter 507 counts up because the data signalDATA₋₋ IN is high. The counter counts up to the maximum value MAX1. Attime T4, when the data DATA₋₋ IN is low, the counter 507 counts down.The counter does not count lower than the minimum count value MIN1.

The integrator 505 utilizes the counter 507 to produce a data signalINT₋₋ OUT. The data signal INT₋₋ OUT transitions from a low to highstate when the count exceeds a threshold value TRH. The threshold valueTRH is, for example:

    TRH=0.9*MAX1

Thus, at time T2, when the count COUNT1 is equal to or greater than thethreshold value TRH, the data signal INT₋₋ OUT becomes high. The datasignal INT₋₋ OUT transitions from a high to low state when the count isequal to a threshold value TRL. The threshold value TRL is, for example:

    TRL=0.1*MAX1

Thus, at time T5, when the count value COUNT1 is equal to or less thanthe threshold value TRL, the data signal INT₋₋ OUT becomes low. In thisway, high frequency components in the data signal DATA₋₋ IN areminimized. As a result, high frequency noise in the data signal DATA₋₋IN is suppressed.

The integrator 505 shifts the data signal INT₋₋ OUT in time with respectto the demodulated signal. The integrator 505 does not significantlyalter the duration of the pulses between the demodulated signal DATA₋₋IN and the data signal INT₋₋ OUT.

Returning to FIG. 9, the processor 315 includes a discriminator 510 thatdifferentiates between ones and zeros in the Manchester encoded datastream. The discriminator includes a re-triggerable counter modulo, forexample, 416 with input value sampling at, for example, count 208. Thediscriminator 510 discriminates between ones and zeros in the Manchesterencoded data in the data signal INT₋₋ OUT. The discriminator 510 alsosynchronizes the internal clock to the clock data in the Manchesterencoded data. The operation of the discriminator 510 is described belowwith reference to FIG. 11. At time T1, a counter 512 located indiscriminator 510 counts up because the data signal INT₋₋ OUT is high.The counter 512 counts up to a maximum value MAX2 and does not exceedthe maximum value MAX2. The maximum value MAX2 is, for example,substantially equivalent to half the expected amplitude of the pulses inthe data signal INT₋₋ OUT.

At time T2, when the count value COUNT1 is greater than or equal themaximum value MAX2, the signal FRESH transitions from a low to a highstate. The transition from the low to high state is used to synchronizethe clock to the Manchester encoded data. The signal produced by thecounter 512 is provided as a data signal SAMPLE to the decoder 515. Thedata signal SAMPLE is either high or low. Thus, at time T1, the datasignal SAMPLE is low. At time T2, the data signal SAMPLE is high. Therising edge of the data signal FRESH indicates that a valid data sampleis provided in data signal SAMPLE. The counter 512 is set, for example,to zero (0) when the data signal INT₋₋ OUT transitions from a high tolow state.

In response to the data signal FRESH and the data signal SAMPLE, thedecoder decodes the Manchester encoded data to retrieve the message datapacket 400 (shown in FIG. 4). The decoder 515 extracts the data from themessage packet 400 and provides it to host computer 320. Alternatively,the decoder may provide the message packet 400 to the host computer 320which extracts the data from the message data packet 400.

The decoder 515 receives the Manchester encoded data and converts it toa message packet 400. In order to convert the Manchester encoded data,the decoder 515 identifies the beginning and the end of the Manchesterencoded data corresponding to the message packet. A start of framesequence is added to the Manchester encoded data by the processor 205during transmission. The start of frame sequence is shown in FIG. 12.The start of frame sequence is a series pulses representing ones andzeros added at the beginning of the Manchester encoded message packet400 (shown in FIG. 4). The start of frame sequence is a combination ofzeros and ones that would not be produced when the message packet 400 isManchester encoded.

Once the start of frame sequence is detected, the decoder 515 determinesthe beginning of the Manchester encoded message packet 400 and decodesit. The end of the Manchester encoded message packet 400 may bedetermined in two ways. If the number of bits of the Manchester encodedmessage packet 400 is known, the decoder 515 may count the number ofbits after receipt of the start of frame sequence. Once the number ofcounted bits equals the number of bits in the Manchester encoded messagepacket, the decoder 515 ignores the remaining bits. Alternatively, anend of frame sequence may be added after the Manchester encoded data bythe tag system 120.

The end of frame sequence is shown in FIG. 13. The end of frame sequenceis a series pulses representing ones and zeros added at the end of theManchester encoded message packet 400 (shown in FIG. 4) by the processor205 during transmission. The end of frame sequence is a combination ofzeros and ones that would be not produced when the message packet 400 isManchester encoded. By using the start of frame sequence and the end offrame sequence, the boundaries of the message packet 400 may bedetermined by the decoder 515. Further, if a collision between messagepackets occurs, one of the message packets may be detected and recoveredby detecting the start of frame sequence. Further, the detection of astart of a second frame sequence indicates that the Manchester encodeddata currently being decoded is invalid and should be ignored. Incontrast, prior art systems utilize illegal Manchester codes to indicatethe start of the encoded data. As a result, if a collision occursbetween transmitted message packets 400 in the prior art systems, it maynot be possible to recover either message packet 400.

Once the decoder 515 retrieves the message packet 400, the decoder 515provides the message packet to host computer 320. Alternatively, theprocessor 315 (shown in FIG. 6) may include additional circuitry and/orsoftware for performing different operations that are implemented by thehost computer 320.

The tag system 120B is protected from tampering such as being removedfrom the vehicle 100. If the tag system 120B is removed from the vehicle100 it could be used to indicate that a vehicle was returned to therental lot. The tag system 120B is protected from tampering by storingdata such as the vehicle identification data in a volatile memory 730 inthe tag system 120B. In this case, the tag system 120B is coupled tobattery 170 (shown in FIG. 2). If the tag system 120B is removed, thetag system 120B is disconnected from the battery 170. Data stored in thevolatile memory 730 within the tag system 120B is lost. For example, thevehicle identification data may be stored in the volatile memory 730.Upon re-applying battery power, the volatile memory 730 is initializedto indicate that the tag system 120B had been previously disconnected.

The car rental system employing the vehicle information system 10simplifies and automates the process of renting, returning, and payingfor rental vehicles especially in large facilities such as airports.Further, the number of individuals utilized at the rental location maybe minimized. For example, the person stationed at the rental area exitmay be eliminated and the number of personnel located at the rental andreturn desks may be reduced.

In an alternative embodiment, vehicle 100 may be located in reserveddedicated short-term parking places, for example, at the airport. Aninterrogator 300A is located on a walkway to the reserved parkinglocations. As the renter passes the interrogator 300A, the interrogatorreceives the data from the driver tag system 120A and determines whichvehicle 100 is to be provided to the renter. Upon determining whichvehicle 100 has been rented to the renter, the interrogator 300Aincludes a display and/or speaker system for informing the renter of thelocation of the vehicle 100.

Another interrogator 300B next to the vehicle 100 receives the datapacket from the driver tag system 120A and releases the keys for thevehicle 100. The interrogator 300B also activates the ignition of thevehicle 100 so that it can be started using the keys. The reservedlocations may be positioned around the short and long term parking areasas well as near rail road, cab, and bus connections.

When the vehicle is returned to the reserved parking, the interrogator300B receives the VID, mileage and fuel level data from the tag system120B and relays this information to the central computer as describedabove. The renter leaves the vehicle 100, approaches the interrogator300B where his tag is read. A key box is opened and the interrogator300B disables the vehicle's ignition. The keys are then placed in thebox, the box closed, and a receipt is printed. The host computer 320also notifies a person to retrieve the vehicle 100. This embodimenteliminates the necessity of boarding a shuttle when picking up ordropping off the vehicle 100.

Although illustrated and described herein with reference to certainspecific embodiments, the present invention is nevertheless not intendedto be limited to the details shown. Rather, various modifications may bemade in the details within the scope and range of equivalents of theclaims and without departing from the spirit of the invention.

What is claimed is:
 1. A vehicle information system in a multiplevehicle environment comprisinga tag system in each vehicle forretrieving data from the vehicle and for only transmitting the retrieveddata, an interrogator for only receiving the retrieved data from eachtag system, and means for avoiding data collisions in said multiplevehicle environment, wherein each tag system transmits the retrieveddata at any time in the multiple vehicle environment and theinterrogator receives the retrieved data from each tag system.
 2. Thevehicle information system of claim 1 includinga single wire data bus insaid vehicle, and a further wire for coupling said tag system to saidsingle wire data bus, wherein said tag system retrieves data from saidvehicle through said further wire.
 3. The vehicle information system ofclaim 1 including a battery in said vehicle, wherein said means foravoiding data collisions includemeans for monitoring a voltage level ofsaid battery, means for transmitting said retrieved data at a rate, andmeans for lowering said rate in response to a drop in said voltagelevel.
 4. The vehicle information system of claim 1 wherein said meansfor avoiding data collisions includemeans for transmitting saidretrieved data in message packets, each message packet transmitted at afixed bit rate, and means for randomly varying the time betweentransmission of each message packet.
 5. The vehicle information systemof claim 4 wherein each of said message packets includes error-detectiondata.
 6. The vehicle information system of claim 4 wherein each of saiddata packets include Manchester coded data.
 7. The vehicle informationsystem of claim 4 wherein said data packets are transmitted at anaverage transmission rate.
 8. The vehicle information system of claim 4wherein said interrogator includes error detection logic for detectingan error in each of said data packets.